Recursion in computer science is when a function calls itself to resolve the problem. Each recursive call usually tries to solve a simpler version of the original problem till we reach a point where the solution is obvious and does not need any further recursive calls.

A probably well known game of Google is that if you search for Recursion that will offer to redirect you to "recursion" again, ad infinitum. Probably the only escape from this is to click on the definition of recursion in Wikipedia